Stable Isotope Profiles Research Articles

A Last Glacial Maximum through middle Holocene stalagmite record of coastal Western Australia climate

Stable isotope profiles of 230Th-dated stalagmites from cave C126, Cape Range Peninsula, Western Australia, provide the first high-resolution, continental paleoclimate record spanning the Last Glacial Maximum, deglaciation, and early to middle Holocene from the Indian Ocean sector of Australia. Today, rainfall at Cape Range is sparse, highly variable, and is divided more or less equally between winter and summer rains, with winter precipitation linked to northwest cloud bands and cold fronts derived from the southern mid- to high-latitudes, and summer precipitation due primarily to tropical cyclone activity. Influences of the Indo-Australian summer monsoon at Cape Range are minimal as this region lies south of the modern monsoon margin. The interaction of these atmospheric systems helps shape the environment at Cape Range, and thus C126 stalagmite-based paleoclimatic reconstructions should reflect variability in moisture source driven by changing ocean and atmospheric conditions.The C126 record reveals slow stalagmite growth and isotopically heavy oxygen isotope values during the Last Glacial Maximum, followed by increased growth rates and decreased oxygen isotopic ratios at 19 ka, reaching a δ18O minimum from 17.5 to 16.0 ka, coincident with Heinrich Stadial 1. The origin of this oxygen isotopic shift may reflect enhanced moisture and lower oxygen isotopic ratios due to amount effect-driven changes in rainfall δ18O values from an increase in rainfall derived from tropical cyclones or changes in northwest cloud band activity, although the controls on both systems are poorly constrained for this time period. Alternatively, lower C126 stalagmite δ18O values may have been driven by more frequent or more intense frontal systems associated with southerly-derived moisture sources, possibly in relation to meridional shifts in positioning of the southern westerlies which have been linked to southern Australia megalake highstands at this time. Finally, we also consider the possibility of contributions of tropical moisture derived from the Indo-Australian summer monsoon. The Intertropical Convergence Zone and associated monsoon trough shifted southward during Heinrich events and other periods of high northern latitude cooling, and although clearly weakened during glacial periods, rainfall with low δ18O values associated with the monsoon today suggests that even small contributions from this moisture source could have accounted for some of the observed oxygen isotopic decrease. Despite a pronounced isotopic excursion coincident with Heinrich Stadial 1, no identifiable anomaly is associated with Heinrich Stadial 2.The Holocene is also characterized by overall low δ18O values and rapid growth rates, with decreasing oxygen isotopic values during the earliest Holocene and at ∼6.5 ka, roughly coincident with southern Australia megalake highstands. The origins of these stalagmite oxygen isotopic shifts do not appear to reflect increases in mean annual temperature but are tied here largely to changes in the δ18O values of precipitation and may reflect a more southerly influence of the Indo-Australian summer monsoon at this time.C126 stalagmite carbon isotopic ratios offer an important complement to the oxygen isotopic time series. Stalagmite δ13C values averaged −5‰ during the Last Glacial Maximum and early deglaciation, and reached a plateau during the oxygen isotopic minimum at 17.5 ka. However, δ13C values decreased sharply to −12‰ between 11 and 8 ka, a shift interpreted to reflect increases in plant density in response to the onset of interglacial conditions. Stalagmite δ13C values at 6 ka are lower than expected for the modern C4-dominated vegetation and thin soils of Cape Range, suggesting that a more C3-rich environment was present during elevated rainfall conditions of the early and middle Holocene. The Cape Range stalagmite time series thus reveals for the first time the millennial-scale sensitivity of the moisture source variations in northwestern Australia, a result that has implications for precipitation dynamics across much of the continent.

Fingerprint and weathering characteristics of crude oils after Dalian oil spill, China

In an attempt to analyze the chemical characterization of oil residues and examine the suitability of chemical fingerprinting methods in oil spill investigations, multiple parameters sensitive to both sources and degree of weathering were used to characterize oil residues from “7–16” Dalian oil spill, China. Oil residues collected 90days to 120days after the spill showed a weathering pattern where significant amounts of light to middle molecular weight normal alkanes were depleted with pristane and phytane as dominant peaks. Diagnostic ratios developed from n-alkane and selected isoprenoids (e.g. Pr/Ph, n-C17/Pr, n-C18/Ph, carbon preference index, LMW/HMW-alkanes ratio), all display obvious changes over weathering time, indicating that these ratios are not valid for oil source identification. Furthermore, the biomarker ratios of hopanes and steranes with relative standard deviations (RSDs) of 0.88–4.08% were useful for source identification even for severely weathered oil residues. In addition, RSD of δ13C values of individual n-alkanes in oil residue varied from 0.07% to 0.20%, which suggest that stable carbon isotope profile of n-alkanes can also be a useful tool for tracing the source of an oil spill.

Identifying recent sources of organic matter enrichment and eutrophication trends at coastal sites using stable nitrogen and carbon isotope ratios in sediment cores

We studied the potential for using stable carbon and nitrogen isotope ratios in sediment profiles to trace external nutrient sources and eutrophication at four coastal sites in the Baltic Sea. The sites are characterized by various present and past activities in their catchments, including residential development, sugar processing, agriculture and fish farming. Radiometrically dated sediment cores were analysed for nutrient isotope ratios, organic carbon and total nitrogen. Background information was collected from historical sources, literature and water monitoring data. Despite the multiple organic enrichment sources, it was possible to identify individual sources and processes in the sediment profiles using stable isotope analysis of bulk sediment. The largest changes in δ15N values were seen at sites receiving urban wastewaters. The site that received effluents from a sugar cane (C4-plant) refinery in the past showed a clear effect on δ13C values compared to the site that received wastewater from a sugar beet (C3-plant) factory. Fish farming produced detectable, albeit minor changes in the sediment profile. Slightly lower δ13C values reflected the influence of fish feed and fish metabolism, and higher δ15N values likely indicated the influence of increased sediment denitrification. The land-sea connection via river discharge was observable in the overall δ13C levels of the sediment cores. Our results suggest that temporal changes in sources of organic matter enrichment can be detected in well-dated coastal sediment cores using nutrient stable isotope analyses, even at sites subjected to multiple impacts. There is not, however, a simple relationship between sediment stable isotope profiles and the eutrophication history of our study sites.

Investigating stock structure and trophic relationships among island-associated dolphins in the oceanic waters of the North Atlantic using fatty acid and stable isotope analyses

Short-beaked common dolphins (Delphinus delphis) and Atlantic spotted dolphins (Stenella frontalis) are the two most abundant cetacean species in the oceanic waters of Madeira and the Azores. They are of similar size, occur in similar habitats and are regularly observed in mixed-species groups to forage together. Genetic analyses suggested that, within each species, dolphins ranging around both archipelagos belong to the same panmictic population. We tested the hypotheses that (1) within each species, individuals from the two archipelagos belong to a single ecological stock; (2) between species, common and spotted dolphins have distinct trophic niches; using fatty acid (FA) and stable isotope (SI) analyses. Fatty acids and stable isotopes were analysed from 86 blubber and 150 skin samples of free-ranging dolphins, respectively. Sex-related differences were not significant, except for common dolphin FA profiles. In S. frontalis, FA and SI differences between archipelagos suggested that individuals belonged to different ecological stocks, despite the existence of gene flow between the two archipelagos. In D. delphis, differences were more pronounced, but it was not possible to distinguish between stock structure and a seasonal effect, due to differential sampling periods in the Azores and Madeira. Inter-specific comparisons were restricted to the Azores where all samples were collected during summer. Differences in FA proportions, noticeably for FA of dietary origin, as well as in nitrogen SI profiles, confirmed that both species feed on distinct resources. This study emphasizes the need for an integrated approach including both genetic and biochemical analyses for stock assessment, especially in wide-ranging marine top predators.

Stable isotope profiling in moderate marine bryozoan colonies across the Isthmus of Panama

In the tropics, upwelling of cold, deep water is the principal source of major seasonal fluctuations in temperature. Along the tropical eastern Pacific (TEP) coast of the isthmus of Panama, seasonal upwelling induces corresponding drops in temperature. Upwelling does not occur along the southwestern Caribbean (SWC) coast of the isthmus. Our goal was to use these oceanographic differences to test the use of stable isotope profiles of free-living modern cupuladriid bryozoans as a method for quantifying paleo-seasonality. We determined O and C stable isotope values from micromilled carbonates profiled along the growth axis in three colonies of Cupuladria exfragminis Herrera-Cubilla, Dick, Sanner and Jackson, 2006 from the upwelling Gulf of Panama in TEP and three colonies of Cupuladria surinamensis Cadee, 1975 from the non-upwelling Bocas del Toro Archipelago in SWC. Pacific colonies had inter-colony [delta]18Ocarb values ranging from -2.1%o to -0.2%o on the international Vienna Pee Dee Belemnite scale, whereas SWC colonies ranged from -1.7%o to -0.6%o. Pacific colonies consistently reveal cyclical trends in [delta]18Ocarb that are absent in the Caribbean colonies. Based on published measurements of temperature, salinity, and [delta]18Osw, the <=2.5 yrs of cyclicity seen in the Pacific colonies reflects a combination of seasonal freshening and seasonal upwelling of colder water. This preliminary study suggests the potential for more exploration of bryozoans as a source of paleoclimate proxies.

Mixing of Rhône River water in Lake Geneva (Switzerland–France) inferred from stable hydrogen and oxygen isotope profiles

Summary Depth profiles were sampled at different locations throughout Lake Geneva on a monthly and seasonal basis over the course of 2 years and analysed for their stable hydrogen and oxygen isotope compositions. The isotopic compositions indicate an isotopic stratification in the metalimnion during summer and fall. This is related to mixing of Rhone River water, which in summer is dominated by snow and glacier melt waters, and lake water, with the latter having a homogenous isotopic composition. The observed interflow layer is 7–15 m thick and can be traced by the distinct stable isotope composition of the water for about 55 km throughout the lake as well as into shallow bay regions. Depth of the interflow layer close to the Rhone River mouth is similar to those previously described based on echo-soundings and turbidity profiles of sediment dispersion. In contrast to previous descriptions of the interflow within Lake Geneva, the stable isotope compositions allow for direct, natural tracing of the Rhone River water even in cases where the turbidity and conductivity measurements do not indicate such an interflow. In addition, the method allows for a quantification of the Rhone River and lake water in the interflow with the fraction of Rhone River water within the interflow estimated to be up to 37% in summer. The isotopic composition further indicates different vertical mixing processes within the two lake basins of Lake Geneva, related to the density gradients and local stability within the water column. The method may be applicable to other lakes in catchments with large differences in the topography as water that originates from high altitudes or glaciers has a distinct oxygen and hydrogen isotope composition compared to other sources of water originating at lower altitudes and/or from direct precipitation over the lake. Stable isotope measurements thus improve the understanding of the circulation of water within the lake, which is fundamental for an evaluation of the water residence times, dissolved pollutant and nutrient transport as well as oxygenation.

Using Isotopic Fractionation to Link Precursor to Product in the Synthesis of (±)-Mephedrone: A New Tool for Combating “Legal High” Drugs

Several recent deaths in the U.K. have been attributed to "legal high" drugs and in particular to (±)-4-methylmethcathinone ((±)-mephedrone). Recent literature has begun to focus on the chemical analysis of mephedrone and related substituted cathinones and methcathinones; however, no studies involving the application of stable isotope analysis to these compounds has yet emerged. Such studies have, for example, the potential to provide information linking the final products to a particular precursor by the manufacturer. In this study, the use of stable isotope profiling was explored to provide a possible connection between product and precursor chemicals. Six samples each of mephedrone were prepared using precursor chemicals from two different manufacturers, providing 12 samples in total. Synthesis was via a stable intermediate.

Holocene climate variability in north-eastern Italy: potential influence of the NAO and solar activity recorded by speleothem data

Abstract. Here we present high-resolution stable isotope and lamina thickness profiles as well as radiocarbon data for the Holocene stalagmite ER 76 from Grotta di Ernesto (north-eastern Italy), which was dated by combined U-series dating and lamina counting. ER 76 grew between 8 ka (thousands of years before 2000 AD) and today, with a hiatus from 2.6 to 0.4 ka. Data from nine meteorological stations in Trentino show a significant influence of the North Atlantic Oscillation (NAO) on winter temperature and precipitation in the cave region. Spectral analysis of the stable isotope signals of ER 76 reveals significant peaks at periods of 110, 60–70, 40–50, 32–37 and around 25 a. Except for the cycle between 32 and 37 a all periodicities have corresponding peaks in power spectra of solar variability, and the 25-a cycle may correspond to NAO variability. This suggests that climate variability in northern Italy was influenced by both solar activity and the NAO during the Holocene. Six periods of warm winter climate in the cave region were identified. These are centred at 7.9, 7.4, 6.5, 5.5, 4.9 and 3.7 ka, and their duration ranges from 100 to 400 a. The two oldest warm phases coincide with the deposition of sapropel S1 in the Mediterranean Sea indicating that the climate in the cave region was influenced by this prominent pluvial phase in the Mediterranean area. For the younger warm phases it is difficult to establish a supra-regional climate pattern, and some of them may, thus, reflect regional climate variability. This highlights the complexity of regional and supra-regional scale Holocene climate patterns.

Precise microsampling of poorly laminated speleothems for U-series dating

One of the principal reasons why speleothems are recognised as important palaeoclimate archives is their suitability for accurate and precise uranium-series (U-series) age determination. Sampling speleothem sections for U-series dating is straightforward in most cases because visible growth layers are preserved. However, this is not always the case, and here we describe a sampling strategy whereby growth layers are resolved from trace-element images produced by laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We apply this method to a section of an Italian subaqueous speleothem (CD3) that lacks persistent visible growth layering.Trace-element imaging revealed growth layers that are strongly non-planar in their geometry owing to the speleothem's pronounced euhedral crystal terminations. The most prominent trace-element layers were first digitized as x, y vector contours. We then interpolated these in the growth-axis direction to generate a series of contour lines at ∼250-μm increments. The coordinates of these contours were used to guide the sampling via a computerised micromilling lathe. This produced a total of 22 samples for U-series dating by multi-collector ICP-MS. The dating results returned ages in correct stratigraphic order within error. Close inspection of the U-series data and the derived depth–age model suggests that the main source of model-age uncertainty is unrelated to the contour sampling but instead more associated with how closely spaced the model ages are in time, i.e. the model age density. Comparisons between stable oxygen and carbon isotope profiles derived from aliquots of the dating samples and two other stable isotope profiles from CD3 spanning the same time period compare very favourably. Taken together, this suggests that our trace-element contouring method provides a reliable means for extracting samples for dating (and other geochemical analyses), and can be applied to similar speleothems lacking visible growth layering.

Dietary Differentiation and the Evolution of Population Genetic Structure in a Highly Mobile Carnivore

Recent studies on highly mobile carnivores revealed cryptic population genetic structures correlated to transitions in habitat types and prey species composition. This led to the hypothesis that natal-habitat-biased dispersal may be responsible for generating population genetic structure. However, direct evidence for the concordant ecological and genetic differentiation between populations of highly mobile mammals is rare. To address this we analyzed stable isotope profiles (δ 13C and δ 15N values) for Eastern European wolves (Canis lupus) as a quantifiable proxy measure of diet for individuals that had been genotyped in an earlier study (showing cryptic genetic structure), to provide a quantitative assessment of the relationship between individual foraging behavior and genotype. We found a significant correlation between genetic distances and dietary differentiation (explaining 46% of the variation) in both the marginal test and crucially, when geographic distance was accounted for as a co-variable. These results, interpreted in the context of other possible mechanisms such as allopatry and isolation by distance, reinforce earlier studies suggesting that diet and associated habitat choice are influencing the structuring of populations in highly mobile carnivores.

Preliminary evaluation of potential stable isotope and trace element productivity proxies in the oyster Crassostrea gigas

As most bivalve mollusks are filter feeders or deposit feeders—predatory septibranchs (Poromyacea) being the notable exception—they are closely linked with the activity of primary producers. Perhaps this is nowhere more evident than in shallow water habitats influenced by seasonal phytoplankton blooms. In these systems, photoautotrophs are capable of changing the physical and chemical properties of the water column. In turn, clams, ingest large quantities of phytoplankton and precipitate their shells in these chemically altered waters. Thus, clam shells likely archive valuable information about phytoplankton dynamics in shallow water habitats. To better understand this relationship, we investigated geochemical records from two potential productivity proxy systems archived in shells of the oyster Crassostrea gigas that live in the San Francisco Bay estuary, California, USA. Here we present multi-year records of shell carbon isotope (δ13Ccarb) and barium/calcium (Ba/Cacarb) variation. These archives are compared with records of environmental variation using oxygen isotopes (δ18Ocarb) as a temporal marker. We also present high-resolution δ13Ccarb, δ18Ocarb and Ba/Ca profiles associated with the 2003 spring phytoplankton bloom. Our results suggest that the prominent positive δ13Ccarb excursion, present in shell material deposited in the spring of 2003, most likely reflects photosynthetic enrichment of the dissolved inorganic carbon pool. Calibration of stable isotopes with calculated chlorophyll a concentrations, measured during the bloom, suggests that our δ13Ccarb sample variation reflects phytoplankton abundance with 3 to 4day resolution. These findings highlight the potential utility of stable isotope records as tools for reconstructing patterns of primary productivity. Elevated Ba/Ca values are recorded each year in the spring. Thus, like stable isotope profiles, Ba/Ca profiles from these specimens demarcate individual years of shell growth and establish ontogenetic age. Low- and high-resolution Ba/Ca profiles do not, however, correlate with the 2003 spring phytoplankton bloom, casting doubt on the relationship between Ba/Ca ratios and phytoplankton blooms. Although the Ba/Ca peak timing loosely correlates with freshwater discharge events, peak amplitude does not, leaving the environmental cause/trigger of these peaks unknown. Nevertheless, the San Francisco Bay estuary seems like an ideal environment in which to further investigate the relationship between skeletal geochemical variation and patterns of primary productivity.

A porewater-based stable isotope approach for the investigation of subsurface hydrological processes

Abstract. Predicting and understanding subsurface flowpaths is still a crucial issue in hydrological research. We present an experimental approach to reveal present and past subsurface flowpaths of water in the unsaturated and saturated zone. Two hillslopes in a humid mountainous catchment have been investigated. The H2O(liquid) – H2O(vapor) equilibration laser spectroscopy method was used to obtain high resolution δ2H vertical depth profiles of pore water at various points along two fall lines of a pasture hillslope in the southern Black Forest, Germany. The Porewater-based Stable Isotope Profile (PSIP) approach was developed to use the integrated information of several vertical depth profiles of deuterium along transects at the hillslope. Different shapes of depth profiles were observed in relation to hillslope position. The statistical variability (inter-quartile range and standard deviation) of each profile was used to characterize different types of depth profiles. The profiles upslope or with a weak affinity for saturation as indicated by a low topographic wetness index preserve the isotopic input signal by precipitation with a distinct seasonal variability. These observations indicate mainly vertical movement of soil water in the upper part of the hillslope before sampling. The profiles downslope or at locations with a strong affinity for saturation do not show a similar seasonal isotopic signal. The input signal is erased in the foothills and a large proportion of pore water samples are close to the isotopic values of δ2H in streamwater during base flow conditions indicating the importance of the groundwater component in the catchment. Near the stream indications for efficient mixing of water from lateral subsurface flow paths with vertical percolation are found.

A refined sampling strategy for intra-tooth stable isotope analysis of mammalian enamel

Serial sampling and stable isotope analysis performed along the growth axis of vertebrate tooth enamel records differences attributed to seasonal variation in diet, climate or animal movement. Because several months are required to obtain mature enamel in large mammals, modifications in the isotopic composition of environmental parameters are not instantaneously recorded, and stable isotope analysis of tooth enamel returns a time-averaged signal attenuated in its amplitude relative to the input signal. For convenience, stable isotope profiles are usually determined on the side of the tooth where enamel is thickest. Here we investigate the possibility of improving the time resolution by targeting the side of the tooth where enamel is thinnest. Observation of developing third molars (M3) in sheep shows that the tooth growth rate is not constant but decreases exponentially, while the angle between the first layer of enamel deposited and the enamel–dentine junction increases as a tooth approaches its maximal length. We also noted differences in thickness and geometry of enamel growth between the mesial side (i.e., the side facing the M2) and the buccal side (i.e., the side facing the cheek) of the M3. Carbon and oxygen isotope variations were measured along the M3 teeth from eight sheep raised under controlled conditions. Intra-tooth variability was systematically larger along the mesial side and the difference in amplitude between the two sides was proportional to the time of exposure to the input signal. Although attenuated, the mesial side records variations in the environmental signal more faithfully than the buccal side. This approach can be adapted to other mammals whose teeth show lateral variation in enamel thickness and could potentially be used as an internal check for diagenesis.

Body size, longevity, and growth rate in Lake Pannon melanopsid gastropods and their predecessors

We investigate potential microevolutionary mechanisms of phenotypic change in a lineage of brackish-water gastropods from Lake Pannon. The lineage exhibits a threefold increase in body size and a pronounced increase in shell shouldering over a roughly 2.5-Myr interval. We use the stable oxygen isotope profiles of 13 shells to address the question of whether large size is due to more rapid growth or to greater longevity.Results indicate that larger individuals have significantly greater longevity. Growth rates in large snails are comparable to those of their smaller-bodied ancestors.Potentially relevant selective advantages of large size include escape from predators, avoidance of resource competition, and increased fecundity. We argue that the first two advantages may have accrued to larger individuals but are not likely to have driven the trend because selection for them would favor more rapid growth rates. Fecundity selection, on the other hand, is readily envisioned in a stable, predictable environment in which the need for early reproduction is relaxed. The evolution of large body size in Lake Pannon molluscs may be comparable to evolution on many islands, where reduced pressure from competition and predation lead to characteristic changes in body size.

Stable isotope profiles of large marine predators: viable indicators of trophic position, diet, and movement in sharks?

Understanding the role of predators is challenging but critical for ecosystem management. For community dynamics, predator-specific size-based variation in diet, trophic position, and habitat use are rarely accounted for. Using two applied tools (stable isotopes and stomach content data), we examined inter- and intra-species ontogenetic variability in diet (stomach contents), trophic position (TPSIA for δ15N and TPSCA for stomach contents), and habitat use (δ13C) of two large sharks, the scalloped hammerhead ( Sphyrna lewini ) and the dusky ( Carcharhinus obscurus ). Stomach contents identified size-based and gender-specific shifts in diet indicating resource partitioning for and between species. Calculated TP for the two sharks varied by method, either TPSIA or TPSCA and with species, size, and gender, but were complicated by differing baselines and broad functional prey groups, respectively. TP increased with size for S. lewini, but was low in large C. obscurus compared with small sharks. Size-based δ13C profiles indicated habitat partitioning by sex in S. lewini and a movement to shelf edge foraging in large C. obscurus. These results demonstrate that predators exert proportional size-based effects on multiple components of the marine system that are further complicated by species- and gender-specific strategies.

Contrasted breeding strategies in four sympatric sibling insect species: when a proovigenic and capital breeder copes with a stochastic environment

Summary1. The evolution of strategies of resource acquisition and allocation is often considered to be closely dependent on the degree of environmental variability. Within this framework, female insects that experience stochastic fluctuations in the availability of their egg‐laying sites in time or space can be expected to be fully synovigenic (i.e. they start maturing eggs after a delay once reaching adulthood), which allows them to tailor their reproductive investment to variations in the resource. Proovigenic females (that have most of their eggs already mature at the onset of their adult life, which corresponds to a capital breeding strategy), on the contrary, should have an advantage when the availability of the egg‐laying sites is predictable. There is, however, a dearth of empirical studies testing these predictions.2. Here, we tested the hypothesis that four phytophagous insect species of the genus Curculio, which coexist on a strongly fluctuating resource that they exploit for egg‐laying purposes, would all be synovigenic as strict proovigeny should be counterselected. The resource consisted of the acorns of oak trees Quercus spp. We conducted field surveys to determine the date of adult emergence in each weevil species and the ability of newly emerged females to produce eggs. We also analysed the stable isotope profile of wild‐caught females as a proxy for their feeding activity. Finally, we tested females under laboratory conditions for their ability to produce mature eggs when not fed and investigated whether dietary intake influenced their longevity.3. Taken together, our results show that, contrary to the usual predictions, the four weevil species that were all exposed to a markedly fluctuating environment exhibited sharply contrasting strategies of resource acquisition and allocation: three species were synovigenic, while the fourth was proovigenic. Unexpectedly, therefore, our findings show that a strict capital breeding species might not always be counterselected in a temporally stochastic environment. They further suggest that fluctuations in the environment should not promote a sole, optimal strategy of energy acquisition and allocation to reproduction but instead should favour their diversification.

Discovery and assembly-line biosynthesis of the lymphostin pyrroloquinoline alkaloid family of mTOR inhibitors in Salinispora bacteria.

The pyrroloquinoline alkaloid family of natural products, which includes the immunosuppressant lymphostin, has long been postulated to arise from tryptophan. We now report the molecular basis of lymphostin biosynthesis in three marine Salinispora species that maintain conserved biosynthetic gene clusters harboring a hybrid nonribosomal peptide synthetase-polyketide synthase that is central to lymphostin assembly. Through a series of experiments involving gene mutations, stable isotope profiling, and natural product discovery, we report the assembly-line biosynthesis of lymphostin and nine new analogues that exhibit potent mTOR inhibitory activity.

Stable isotope profiles in whale shark (Rhincodon typus) suggest segregation and dissimilarities in the diet depending on sex and size

We investigated the sex- and size-related differences in the diet of whale sharks from the Arabian Sea (north-western Indian Ocean) using carbon and nitrogen stable-isotope analyses in white muscle. The samples were collected during the commercial fishing season between April and May of 2001 in Veraval (Gujarat, India). The overall isotope signature was similar to that of the pelagic-neritic zooplanktivore Ilisha melastoma, which suggests that both species are feeding on similar prey. In whale sharks, a positive relationship was found between δ15N and δ13C. This, together with a significant enrichment of both heavy stable isotopes with total length indicates that the contribution to the diet of small fish and/or larger zooplankton of higher trophic level increases with the movement from offshore areas to coastal areas as they grow. Gender differences in the isotopic ratios were not statistically significant, but small sample size cannot rule out completely the existence of some degree of spatial or dietary segregation between sexes.

Stable isotope profiles of nitrogen gas indicate denitrification in oxygen‐stratified humic lakes

Mid-summer N(2) profiles were analyzed from nine oxygen-stratified, humic-acid-rich lakes using a continuous flow isotope ratio mass spectrometer and a Gasbench II device. Sample preparation steps were performed under water to avoid air contamination. The instrument precision for the δ(15)N measurement was high (0.03‰), but for the whole sampling and analysis procedure the mean deviation between replicate samples was 0.13‰ for the δ(15)N measurements and 5.5% for the N(2) gas concentration analysis. The results show that the Gasbench peripheral was suitable for measurement of the (15)N natural abundance of dissolved nitrogen gas, with denitrification indicated by the oversaturation and slightly (<1‰) depleted δ(15)N values of the dissolved N(2) gas in the suboxic zones of some of the study lakes. Calculated values for the denitrified (excess) N(2) varied between -5.3 and 0.7‰. The denitrification potential was determined using the (15)N tracer method, with results showing nitrate-inducible denitrification and no signs of anaerobic ammonium oxidation (anammox).

Abrupt millennial-scale changes in intensity of Southern Hemisphere westerly winds during marine isotope stages 2–4

Research Article| May 01, 2011 Abrupt millennial-scale changes in intensity of Southern Hemisphere westerly winds during marine isotope stages 2–4 Thomas E. Whittaker; Thomas E. Whittaker * 1Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand *Current address: Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA; E-mail: twhittak@unm.edu. Search for other works by this author on: GSW Google Scholar Chris H. Hendy; Chris H. Hendy 1Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand Search for other works by this author on: GSW Google Scholar John C. Hellstrom John C. Hellstrom 2School of Earth Sciences, University of Melbourne, VIC 3010, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information Thomas E. Whittaker * 1Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand Chris H. Hendy 1Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand John C. Hellstrom 2School of Earth Sciences, University of Melbourne, VIC 3010, Australia *Current address: Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA; E-mail: twhittak@unm.edu. Publisher: Geological Society of America Received: 14 Oct 2010 Revision Received: 12 Dec 2010 Accepted: 14 Dec 2010 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2011 Geological Society of America Geology (2011) 39 (5): 455–458. https://doi.org/10.1130/G31827.1 Article history Received: 14 Oct 2010 Revision Received: 12 Dec 2010 Accepted: 14 Dec 2010 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Thomas E. Whittaker, Chris H. Hendy, John C. Hellstrom; Abrupt millennial-scale changes in intensity of Southern Hemisphere westerly winds during marine isotope stages 2–4. Geology 2011;; 39 (5): 455–458. doi: https://doi.org/10.1130/G31827.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The strength of mid-southern latitude westerly atmospheric circulation plays an important role in global climate. Due to a lack of long, continuous, high-resolution paleoclimate archives from mid-southern latitudes, it remains unclear what factors control changes in its intensity and how past changes affected the climates of landmasses in their path. Here we show growth rate and stable isotope (δ18O, δ13C) profiles from a South Island, New Zealand, stalagmite (HW3) that permit centennial-scale investigation of Southern Hemisphere westerly paleointensity between 73 and 11 ka. Correlation between HW3 growth rate and isotope profiles suggests sensitivity to changes in annual precipitation, a factor controlled by westerly intensity. Low growth rates and relatively enriched isotope ratios define long-term trends in HW3, supporting existing evidence that weaker westerlies predominated during the last glacial period. Abrupt millennial-scale events occur frequently, such that the HW3 record resembles Greenland ice core stable isotope profiles. Furthermore, nearly synchronous timing of nine prominent wet and cool intervals with Heinrich events supports studies showing that increased westerly intensity is closely linked to North Atlantic cooling. As well as Heinrich events, the HW3 profiles also show an Antarctic Cold Reversal–like event during deglaciation, advocating for a bipolar seesaw of global climate at that time. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.